Re: [PATCH RFC 1/6] mm, slab: make caches with refcount of 0 unmergeable

[David Rientjes]

On Mon, 15 Jul 2024, Vlastimil Babka wrote:

> Slab caches with refcount 0 are in the process of being destroyed so
> it's undesirable for new caches to attempt merging with them. A
> synchronous destruction happens under slab_mutex thus excluding
> concurrent cache creation and merging. Full destruction of
> SLAB_TYPESAFE_BY_RCU caches might be delayed, but the cache is still
> taken off the slab_caches list immediately, thus unreachable by cache
> creation.
> 
> However a cache where __kmem_cache_shutdown() fails because it contains
> objects that were not freed (due to a bug in the cache user) will be
> left on the slab_caches list and might be considered for merging.
> Also the following patches will introduce a possibility of a cache with
> refcount 0 being temporarily reachable on the slab_list even in case of
> no bugs, due to kfree_rcu() in flight.
> 
> For these reasons, prevent merging with caches that have zero refcount.
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>